1. Field of the Invention
The present invention relates generally to the field of signal processing and, in particular, to a programmable filter apparatus for applying a frequency response to an input signal to produce a filtered output signal.
2. Description of the Related Art
Filters of various types and configurations are commonly used components in most signal processing applications. A typical filter is designed to apply a fixed frequency response to an input signal to produce a different filtered output signal. Traditionally, a filter is implemented as a discrete element or component on a circuit board of an electronic device. Since a filter contributes to the functionality and operational characteristics of the electronic device, if the functionality and/or characteristics of the electronic device need to be changed then the filter installed in the electronic device may need to be replaced with another filter having a different desirable frequency response.
Replacement of a filter often involves manually detaching the filter from the circuit board of the electronic device and then soldering, or otherwise attaching the replacement filter, while taking care not to damage the filters or other device components. Thus, replacement of an installed filter is an undesirable, time consuming and challenging task that may result in damage to installed or replacement filters or to other device components.
To address this problem, tunable variable frequency filters have been developed. A tunable filter may be adjusted to vary its frequency response within a predefined frequency response range. Thus, if the functionality or operational characteristics of the electronic device are to be changed, the tunable filter may be adjusted as needed or appropriate to provide the desired new frequency response for the electronic device. However, tunable filters have several significant disadvantages. First, these are relatively bulky and are thus difficult to position and install on circuit boards of most electronic devices, where space is often at a premium. The size of tunable filters makes them unusable in many signal processing applications which require compact or miniaturized circuitry. Second, tunable filters are much more expensive than their fixed frequency counterparts. Finally, tunable filters have a lower Q-factor (quality factor) than fixed frequency filters.
Thus, it would be desirable to provide a small-sized, inexpensive programmable filter having an adjustable frequency response and having a high quality factor comparable to that of fixed frequency filters.